Black dot disease detected in P.E.I. potato crops

A fungal disease that affects plant tissues has been detected in Prince Edward Island potato crops.

Black dot disease — named for the fine black spots that appear on infected roots, stems and leaves — is typically brought in on infected seed and spreads through soil, said Julie Pasche, associate professor and chair of potato pathology at North Dakota State University. 

Pashe said that once the pathogen is in a field it will remain in the field for quite some time and build up with each additional potato crop.

"They are very durable structures that survive in the soil," she said. "They're not broken down very easily."

Black dot isn't thought to be widespread on the Island, but growers are keeping an eye out for it, said the P.E.I. Potato Board. 

Pasche ran a session on the emergence of black dot at the P.E.I. Potato Conference earlier this month. 

There are two phases of black dot: the foliar phase and the tuber blemish phase, Pasche said. 

The foliar phase "really ties in with the early-die complex," which is also caused by other diseases like verticillium wilt.

That could result in yield loss and smaller tubers, which would affect processing growers, she said. 

The second phase is especially important for fresh table stock growers, Pasche said. That phase causes discolouration.

"If you're in the grocery store, [they] wouldn't necessarily be the ones that you would choose." 

Black dot can be seen with the naked eye, but it can sometimes be difficult to spot.

It can look very similar to other diseases, Pasche said. "The most important thing is to be able to discern the symptoms and signs of black dot." 

When it comes to eliminating the disease, Pasche said the best method is to let land lie fallow for 15 to 20 years, depending on how much of the pathogen is in the soil.